Fuse



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Feb. 21, 1933.

Patented Feb. 21, 1933 UNITED STATES PATENT OFFICE JEROME SANDIN, OF WILKINS TOWNSHIP, .ALLEGHENY COUNTY, E'NNSYL'VANIA,

a.ASSIGNOR TO WESTINGQHOUSE ELECTRIC & MANUFACTURING COMPANY, .A CORPO- RATION OF PENNSYLVANIA FUSE Appnction mea iray 12, 1927. ser-m1 No. 190,679.

My invention relates to circuit interrupters and more particularly to fuses.

One object of my invention is to provide a fuse `element that shall have sufficient strength to support a biasing spring.

Another object of my invention is to provide a fuse element biased by a spring member that shall not be distorted by repeated overloads, the values of which are too low to cause rupture of the fuse element.

A further object of my ,invention is to provide a fuse element that shall be capable of rupturing when an overload of predetermined value exists in the circuit, but shall have sufficient strength to support a biasing spring member without being distorted.

Prior art discloses the employment of a I tension spring for moving a portion of the fuse element, after rupture, away from the terminal portion, thus elongating the arc and materially aiding its extinction. Arc extinguishing liquids, such as pyrene, Carbon tetra-chloride, oil or the like have been employed in the body of fuse containers of the prior art through which the'arc is drawn by a. biasing spring to extinguish it. Difficulty has always been experienced in obtaining a fuse element that is able to support the pull of the biasing spring member without being distorted by the repeated slight overloads that are present in the circuit from time to time. When a fuse element of the type employed in fuses which have no such biasing spring is 'utilized in fuses so biased, the repeated slight ovrloads heat the fuse element, thereby softening it and, owing to its being under tension of the biasing spring, it elongates, reducing the cross-section of the portion so heated. As the current rating of a fuse of a given material depends upon its cross section, it naturally follows that the reduction of cross-section above indicated will cause the fuse element to rupture prematurely.

Several means are now employed to prevent such changes; for example, the employment of a thin wire having great tensile strength looped about the fuse element to take the tension of the biasing spring therefrom. In

- a fuse element of this type, when a current overload is present in the circuit, the fuse element is melted first, thereby leaving the thin wire above in the circuit with the Consequence that it is immediately fused. An objection to this type of fuse element is that the high temperatures resulting from repeated overloads too small to cause rupture of the element are harmful-to the are quenching liquid in that it is deteriorated and evaporated thereby.

I In practicing my invention, I propose to overcome the aforesaid difculty by employing a fuse element which comprises two pieces of a material of nigh melting point and of relatively large cross section soldered together with a metal having a lower melting point. Under slight overloads, the heat produced in the fuse element will cause the fuse elements to part at the soldered section, while a-short-circuit will cause rupture in an adjoining part of reduced cross section.

In the accompanying drawing,

Figure l is a view in section embodying a preferred form of my invention.

Fig. 2 is a broken view in sect-ion taken a 90 degrees to that of Fig. 1.

Fig. 3 is a broken view in section embodying a modification of my invention, and

Fig. 4 isa broken View in section embodyin still another form of my invention.

y invention comprises, in genera-l, a fuse element 1 constituted by portions 2 and 4, which are soldered together at 5 to makea single uni-t. The portion 2 has a hole 3 therein to provide a reduced cross sectional area.

This fuse element will not only be ruptured by currents of high value at the reduced cross section, but will also separate at the soldered section in the presence of a current of low value that has been present inthe circuit for some time, in a manner hereinafter explained.

In Figs. 1 and 2, the fuse element 1 is supported within an outer casing 6 that has ferrules 7 and 8 attached to its ends. The ferrules 7 and 8 are threaded to take end caps 9 and 10, respectively, to entirely enclose the outer casing 6. The fuse element 1 projects through a hole 11 in a washer 12 that rests on the top of the outer casing 6 and has a right-angled portion 13 clamped between the washer 12 and the end cap 8 and is rigidly supported thereon. The other end of the fuse element 1 supports the end of a tension spring 14 and an end of a Hexible shunt 15 that is attached to a terminal 16 which in turn is supported by bolt 17 to the fuse element 1. The lower end of the tension spring 14 and the flexible shunt 15 are permanently supported on a Washer 18 that is held on the lower portion of the outer Casing 6 by the end cap 10. The interior 19 of the outer casing 6 contains an arc quenching liquid 2O such as oil, carbon-tetra chloride or the like, that is employed to extin- Qguish the arc after it is drawn therein by the action of the tension spring 14.

Fig. 3 is a modification of my invention in which a fuse element 21 is constituted vby a portion 22 that has a fusible section 23 of desired rating and a washer portion 24 that is soldered by metal 25 to a supporting washer 26, being biased and supported in the same manner as-disclosed in the structure infFigs. 1 and 2. A

Fig. 4 is a further modification of my invention, in which a'fuse element 27 is co1- stituted by a fusible portion 28 that is soldered by metal 29 to a supporting washer 31. The-lower end of the fusible portion 28 supports the biasing spring and iexible shunt in a manner described in Figs'. 1 and 2.

In the arrangements just described, the fuse element proper is constituted by portions 2, 4 and 5 in Fig.l 1, portions 22 to 26\ in Fig. 3, and portions 28, 29 and 31 in Fig. 4, respectively. These are known as refills as they arethe expendible portion of the fuse that may be renewed by .the insertion of a new one in ru tured. i

imple means, common in the art, arepro'- vided to support the refill nin the circuit so that renewal in the field can be accomplished with a minimum expenditure of time and energy.

The hole 3 or other cross section-reducing l means is employed inthe body of the fuse element 1, adjoining the soldered section 5, to localize the point of fusion when a shortcircuit occurs in the circuit. The object'of this is, to provide a section having'a small thermal capacity that will be heated andv ruptured by an increase in current so rapid that the relatively vgreatpmass of the soldered section 5 would prevent it from being sufiioiently heated to rupture.

The soldered portion 5 is chosen to have a largel heat absorbing capacity coupled, with low heat radiating ability, so that in the presence of overloads .only slightly in excess of therating of the fuse, heat will be stored in the soldered ,section 5, and, due to its low radiatingability, the temperature will increase with time, causing a sufficient rise the place of the one eventually to melt the solder therein and thereby cause the circuit to be interrupted.

The heat produced by such an overload l would'not be sufficient to rupture the adj oin--q ing reduced or fusible section at hole 3, as its high radiatingability would'prevent an accumulatioof heat therein.

Assume the fuse 1 to be in operating conre'nt will flow through the end cap 10, washer 18 through the iexible shunt 15, terminal 16 to the fuse element 1, then to the cap 9 and the other branch of the circuit to be protected. When a 'short circuit occurs in the said circuit, the fuse element 1, in Figs. 1 and 2, will be immediately ruptured adjacent hole 3 by thecomparatively large current and the arc formed thereby will be elongated by the action of the tension spring 14that draws it into :the arc-extinguishing liquid 20 contained within the outer casing 6. The soldered section 5 would not be heated to its melting point in the short time available because of its large thermal capacity.

In a structure similar to that in Fig. 3, fusible section 22 would be ruptured and the arc would be extinguished vin a similar manner. In the structure in Fig. 4, a fusible portion 28 would be ruptured and the arc similarly extinguished. The operation of the fuse element as described above is 'similar to that in fuses which have heretofore been employed in the art.

In case an overload of small current value is present in the circuit, rupturing of the above said fusible portion- 3 would nottake place,but the soldered section 5 would become heated, the degree of this heating depending upon the value of the increased current, the' duration of its presence in the circuit and the heat absorbing and radiating properties of the material. The soldered section 5 containing `considerable mass has good heat absorbing, but low radiating properties as a result of which its increase in temperature will vary with the amount and duration of the overload. After a suflicient time has elapsed, the heat input in the soldered section 5 will havev raised its temperature sufficiently to melt the solder and permit the sections 3 and 4 of the fuse element 1 to separate.

The reduced or fusible section at the hole 3 -of the fuse elementV 1 would not be affected by this small overload of appreciable duration as the heat produced thereat would be i that of the soldered section 5, would slowly l but surely reach the fusing point. That is, as the melting point of the fusible element at the hole 3 is greater than at the soldered section 5, the temperature at the hole 3 may increase sufficiently to radiate and conduct heat away as rapidly as it is produced, without reaching the melting point.

In the case of a short-circuit condition being present in the circuit, the greatly increased amount of current produces so rapid an increase of temperature in the fuse element l that the reduced or fusible section at the hole 3 will absorb heat much faster than it can be radiated or conducted away, resulting in the temperature risin much more ra idly in the reduced or fusi le section at t e hole 3 than in the soldered section 5. As a consequence the former will be fused before the temperature in the soldered section 5 canv be raised sufliciently to cause the separation at that point.

In designing a fuse element l of this type, selection must be made in the kinds of material and the relative size of the fusible and the soldered section, so that an increase in current can never produce such an increase intemperature as will heat the fusible section at the hole 3 to apoint where it will stretch under the action of the biasing spring, Without causing separation at the soldered section 5. It will be noted that a soldered joint between two metal plates gives way suddenly at the melting point without appreciable softening or stretching at lower temperatures.

It therefore follows that I have invented a fuse element that is ablel to withstand the tension of a biasing spring which it supports and will not be distorted or have its calibra tion reduced by the presence of overloads of small current value that are impressed from time to time in the circuit. Before the overload has reached a value sufficient to produce an amount of heat in the fuse element to cause the elongation of the fusible portion and thereby reducing its cross-sectional area and calibration, the soldered section supported by Y a metal having a predetermined melting point will be separated and the circuit will be interrupted.

It may be noted that since the amount of metal required to dissipate the heat generated by a given current is lessened if the metal can run at a high temperature, I may make the conductor having the reduced section at the hole 3 of a higher melting metal in order vto attain the combination of small mass with large heat-dissipating power desired at that point as above described. On the other hand no such reasoning applies to the solder at 5 and it may be made of readily fusible metal. My invention therefore insures overload protection for high or low current values and is able to retain its proper calibration in the presence of overloads of small valuev that could have no harmful effect on the apparatus protected due to high temperature.

can be melted by a small increase in current of long duration, one of said members having a reduced section that is ruptured before the solder can be melted when the current therethrough has rapidly increased to a large value.

2. The combination in a fuse structure constituted by a body portion and end closures, of a fuse element comprising two sections of metal more refractory than solder soldered together and supported at one end within the said body portion, one of said sections having a portion of reduced area separate from the soldered portion and a biasing spring attached to the unsupported end of the said fuse element for elongating the arc after the rupturing of the fuse element at the reduced or soldered section. .v

3. The combination in a fuse structure constituted by a body portion and end closures, of a fuse element having a calibrated section of reduced area and a soldered section separate therefrom, said fuse element being supported at one end within the said body portion, and a biasin spring attached to the unsupported end o the said fuse element for elongating the arc after the rupturing of thel fuse element at either the reduced or the soli dered section.

4. The combination in a fuse structure constituted by a body portion and end closure, of a fuse element having a plurality of sections of metal more refractory than solder soldered together and supported at'one of its ends near an end closure, one of said sections having a reduced area separate from said soldered portion and a biasing spring supported at the other end closure and attached to the unsupported end of the fuse element.

5. A fuse element for an electrical circuit, said fuse element including two sections of metal soldered together, the metal of each` of said sections being more refractory than the solder securing them together, one of said sections having avportion of reduced cross sectional area separate from the soldered portion, both said soldered portion and said reduced portion being fusible to rupturethe current through said fuse element.

6. A renewable fuse element for an electrical fuse in which the fuse element is stressed in tension, said fuse element having a section of reduced cross-sectional area and an adjacent soldered section of increased area, each of said sections being fusible by a different ifncreased current condition through said use'. v V 7.- A fusible element forY a fuse having a first fusible part and a second fusible part of higher melting point than the Vfirst part, the cross-sectional area of the :second part being reduced to the extent that the passage of eX.- cess current will generate therein the amount ofheat necessary to fuse the same before generating in the first part the amount of heat to fuse the latter, whereby upon short circuit the second part will be first fused and upon overload the dissipation of heat from the second element will prevent the same from acquiring fusing temperature while the firstv part will reach its lower melting point by the accumulation of heat. r

In'testimony whereof, I have hereunto subsdribed my name this 3rd day of May, 1927.

' JEROME SANDIN. 

